The invention relates to an electrically weldable spring hinge according to the preamble of Claim 1.
Spring hinges of the type discussed herein are known. Such spring hinges are used as hinges for eyeglasses, and by use of an electric welding process are fastened to the earpieces or the center part of an eyeglass. Spring hinges include a housing which is open at a bottom side and has a cavity in which a spring element is situated. Also provided in the housing are at least one support element and a hinge element which is displaceably supported in the housing. For electric welding the bottom side of the spring hinge is firmly pressed against an eyeglass element, for example an earpiece. The contact pressure is in the range of 70 to 700 N, for example. As soon as the contact forces are applied, a welding current of 2000 A to 8000 A is passed through the housing of the spring hinge and the eyeglass element, i.e., the earpiece or the center part of an eyeglass. In the contact region between the spring hinge and the earpiece weld buttons are provided which heat up and melt under the high current intensities. A secure connection between the spring hinge and the eyeglass element is produced in this manner. It has been found that under the high contact forces deformation of the housing of the spring hinge may occur, in particular in the cavity provided inside the housing which is used to accommodate the spring element, the hinge element, and the support element. During electric welding, material deposits may also occur which impair optimal functioning of the spring hinge. The material inside the housing, namely in the cavity, may be displaced, resulting in a protrusion at that location. If the housing and thus the cavity undergoes deformation, the mobility of the hinge element relative to the housing, and therefore the functioning of the spring hinge, is impaired. Such deformations of the housing occur in particular in small spring hinges which are finding increasing use.